Characteristic features of parrots include a strong, curved bill, an upright stance, strong legs, and clawed zygodactyl feet. Many parrots are vividly coloured, and some are multi-coloured. The plumage of cockatoos ranges from mostly white to mostly black, with a mobile crest of feathers on the tops of their heads. Most parrots exhibit little or no sexual dimorphism. They form the most variably sized bird order in terms of length.

The most important components of most parrots' diets are seeds, nuts, fruit, buds and other plant material. A few species sometimes eat animals and carrion, while the lories and lorikeets are specialised for feeding on floral nectar and soft fruits. Almost all parrots nest in tree hollows (or nest boxes in captivity), and lay white eggs from which hatch altricial (helpless) young.

Parrots, along with ravens, crows, jays and magpies, are among the most intelligent birds, and the ability of some species to imitate human voices enhances their popularity as pets. Trapping wild parrots for the pet trade, as well as hunting, habitat loss and competition from invasive species, has diminished wild populations, with parrots being subjected to more exploitation than any other group of birds.[6] Measures taken to conserve the habitats of some high-profile charismatic species have also protected many of the less charismatic species living in the same ecosystems.[7]

Contents

Psittaciform diversity in South America and Australasia suggests that the order may have evolved in Gondwanaland, centred in Australasia.[8] The scarcity of parrots in the fossil record, however, presents difficulties in supporting the hypothesis.

It is now generally assumed that the Psittaciformes, or their common ancestors with several related bird orders, were present somewhere in the world around the Cretaceous–Paleogene extinction event (K-Pg extinction), some 65 Ma If so, they probably had not evolved their morphologicalautapomorphies yet, but were generalised arboreal birds, roughly similar (though not necessarily closely related) to today's potoos or frogmouths (see also Palaeopsittacus below). Though these birds (Cypselomorphae) are a phylogenetically challenging group, they seem at least closer to the parrot ancestors than, for example, the modern aquatic birds (Aequornithes). The combined evidence supported the hypothesis of Psittaciformes being "near passerines", i.e. the mostly land-living birds that emerged in close proximity to the K-Pg extinction. Indeed, analysis of transposable element insertions observed in the genomes of passerines and parrots, but not in the genomes of other birds, provides strong evidence that parrots are the sister group of passerines, forming a clade Psittacopasserae, to the exclusion of the next closest group, the falcons.[9]

Europe is the origin of the first presumed parrot fossils, which date from about 50 Ma. The climate there and then was tropical, consistent with the Paleocene-Eocene Thermal Maximum. Initially, a neoavian named Mopsitta tanta, uncovered in Denmark's Early EoceneFur Formation and dated to 54 Ma, was assigned to the Psittaciformes; it was described from a single humerus.[10]
However, the rather nondescript bone is not unequivocally psittaciform, and more recently it was pointed out that it may rather belong to a newly-discovered ibis of the genus Rhynchaeites, whose fossil legs were found in the same deposits.

Fossils assignable to Psittaciformes (though not yet the present-day parrots) date from slightly later in the Eocene, starting around 50 Ma. Several fairly complete skeletons of parrot-like birds have been found in England and Germany.[11] Some uncertainty remains, but on the whole it seems more likely that these are not direct ancestors of the modern parrots, but related lineages which evolved in the Northern Hemisphere and have since died out. These are probably not "missing links" between ancestral and modern parrots, but rather psittaciform lineages that evolved parallel to true parrots and cockatoos and had their own peculiar autapomorphies:

The earliest records of modern parrots date to about 23–20 Ma and are also from Europe. Subsequently, the fossil record—again mainly from Europe—consists of bones clearly recognisable as belonging to parrots of modern type. The Southern Hemisphere does not have nearly as rich a fossil record for the period of interest as the Northern, and contains no known parrot-like remains earlier than the early to middle Miocene, around 20 Ma. At this point, however, is found the first unambiguous parrot fossil (as opposed to a parrot-like one), an upper jaw which is indistinguishable from that of modern cockatoos. A few modern genera are tentatively dated to a Miocene origin, but their unequivocal record stretches back only some 5 million years (see genus articles for more).

The Strigopoidea were considered part of the Psittacoidea, but recent studies place this group of New Zealand species at the base of the parrot tree next to the remaining members of the Psittacoidea as well as all members of the Cacatuoidea.[8][13][14]

The Cacatuoidea are quite distinct, having a movable head crest, a different arrangement of the carotid arteries, a gall bladder, differences in the skull bones, and lack the Dyck texture feathers which, in the Psittacidae, scatters light in such a way as to produce the vibrant colours of so many parrots. Colourful feathers with high levels of psittacofulvin resist the feather-degrading bacteriumBacillus licheniformis better than white ones.[15]

The most obvious physical characteristic is the strong, curved, broad bill. The upper mandible is prominent, curves downward, and comes to a point. It is not fused to the skull, which allows it to move independently, and contributes to the tremendous biting pressure the birds are able to exert. The lower mandible is shorter, with a sharp, upward-facing cutting edge, which moves against the flat portion of the upper mandible in an anvil-like fashion. There are touch receptors along the inner edges of the kerantinised bill, which are collectively known as the 'bill tip organ', allowing for highly dextrous manipulations. Seed-eating parrots have a strong tongue (containing similar touch receptors to those in the bill tip organ), which helps to manipulate seeds or position nuts in the bill so that the mandibles can apply an appropriate cracking force. The head is large, with eyes positioned high and laterally in the skull, so the visual field of parrots are unlike any other birds. Without turning its head, a parrot can see from just below its bill tip, all above its head, and to quite far behind its head. Parrots also have quite a wide frontal binocular field for a bird, although this is nowhere near as large as primate binocular visual fields.[21]

Parrots have strong zygodactyl feet with sharp, elongated claws, which are used for climbing and swinging. Most species are capable of using their feet to manipulate food and other objects with a high degree of dexterity, in a similar manner to a human using his hands. A study conducted with Australian parrots has demonstrated that they exhibit "handedness"—that is a distinct preference with regards to the foot used to pick up food, with adult parrots being almost exclusively "left-footed" or "right footed", and with the prevalence of each preference within the population varying from species to species.[22]

Cockatoo species have a mobile crest of feathers on the top of their heads which can be raised for display, and retracted. No other parrots can do so, but the Pacific lorikeets in the genera Vini and Phigys are able to ruffle the feathers of the crown and nape and the Red-fan Parrot (or Hawk-headed Parrot) has a prominent feather neck frill which can be raised and lowered at will. The predominant colour of plumage in parrots is green, though most species have some red or another colour in small quantities. Cockatoos are the main exception to this, having lost the green and blue plumage colours in their evolutionary history they are now predominately black or white with some red, pink or yellow. Strong sexual dimorphism in plumage is not typical among parrots, with some notable exceptions, the most striking being the Eclectus Parrot.

Parrots are found on all tropical and subtropical continents including Australia and Oceania, South Asia, Southeast Asia, Central America, South America and Africa. Some Caribbean and Pacific islands are home to endemic species. By far the greatest number of parrot species come from Australasia and South America. The lories and lorikeets range from Sulawesi and the Philippines in the north to Australia and across the Pacific as far as French Polynesia, with the greatest diversity being found in and around New Guinea. The subfamily Arinae encompasses all the Neotropical parrots, including the Amazons, macaws and conures, and ranges from northern Mexico and the Bahamas to Tierra del Fuego in the southern tip of South America. The pygmy parrots, tribe Micropsittini, form a small genus restricted to New Guinea. The superfamily Strigopoidea contains three living species of aberrant parrots from New Zealand. The broad-tailed parrots, subfamily Platycercinae, are restricted to Australia, New Zealand and the Pacific islands as far eastwards as Fiji. The true parrot superfamily, Psittacoidea, includes a range of species from Australia and New Guinea to South Asia and Africa. The centre of cockatoo biodiversity is Australia and New Guinea, although some species reach the Solomon Islands (and one formerly occurred in New Caledonia),[23]Wallacea and the Philippines.

There are numerous challenges in studying wild parrots, as they are difficult to catch and once caught they are difficult to mark. Most wild bird studies rely on banding or wing tagging, but parrots will chew off such attachments.[29] Parrots also tend to range widely and consequently there are many gaps in knowledge of their behaviour. Some parrots have a strong, direct flight. Most species spend much of their time perched or climbing in tree canopies. They often use their bills for climbing by gripping or hooking on branches and other supports. On the ground parrots often walk with a rolling gait.

The diet of parrots consists of seeds, fruit, nectar, pollen, buds, and sometimes arthropods and other animal prey. The most important of these for most true parrots and cockatoos are seeds; the evolution of the large and powerful bill can be explained primarily as an adaptation to opening and consuming seeds. All true parrots except the Pesquet's Parrot employ the same method to obtain the seed from the husk; the seed is held between the mandibles and the lower mandible crushes the husk, whereupon the seed is rotated in the bill and the remaining husk is removed.[29] A foot is sometimes used to help holding large seeds in place. Parrots are seed predators rather than seed dispersers; and in many cases where species are recorded as consuming fruit they are only eating the fruit to get at the seed. As seeds often have poisons to protect them, parrots are careful to remove seed coats and other fruit parts which are chemically well defended, prior to ingestion. Many species in the Americas, Africa, and Papua New Guinea consume clay which both releases minerals and absorbs toxic compounds from the gut.[30]

The lories and lorikeets, hanging parrots and Swift Parrot are primarily nectar and pollen consumers, and have tongues with brush tips to collect this source of food, as well as some specialised gut adaptations to accommodate this diet.[31] Many other species also consume nectar as well when it becomes available.

Although there are a few exceptions, parrots are monogamous breeders which nest in cavities and hold no territories other than their nesting sites.[29][35] The pair bonds of the parrots and cockatoos are strong and a pair will remain close even during the non-breeding season, even if they join larger flocks. As with many birds, pair bond formation is preceded by courtship displays; these are relatively simple in the case of cockatoos. In Psittacidae parrots common breeding displays, usually undertaken by the male, include slow deliberate steps known as a "parade" or "stately walk" and the "eye-blaze", where the pupil of the eye constricts to reveal the edge of the iris.[29]Allopreening is used by the pair to help maintain the bond. Cooperative breeding, where birds other than the breeding pair help the pair raise the young and is common in some bird families, is extremely rare in parrots, and has only unambiguously been demonstrated in the Golden Parakeet (which may also exhibit polyamorous, or group breeding, behaviour with multiple females contributing to the clutch).[36]

Only the Monk Parakeet and five species of Agapornis lovebird build nests in trees,[37] and three Australian and New Zealand ground parrots nest on the ground. All other parrots and cockatoos nest in cavities, either tree hollows or cavities dug into cliffs, banks or the ground. The use of holes in cliffs is more common in the Americas. Many species will use termite nests, possibly to reduce the conspicuousness of the nesting site or to create a favourable microclimate.[38] In most cases both parents will participate in the nest excavation. The length of the burrow varies with species, but is usually between Template:Convert/–Template:Convert/test/Aon in length. The nests of cockatoos are often lined with sticks, wood chips and other plant material. In the larger species of parrot and cockatoo the availability of nesting hollows may be limited, leading to intense competition for them both within the species and between species, as well as with other bird families. The intensity of this competition can limit breeding success in some cases.[39][40] Some species are colonial, with the Burrowing Parrot nesting in colonies up to 70,000 strong.[41] Coloniality is not as common in parrots as might be expected, possibly because most species adopt old cavities rather than excavate their own.[42]

The eggs of parrots are white. In most species the female undertakes all the incubation, although incubation is shared in cockatoos, the Blue Lorikeet, and the Vernal Hanging Parrot. The female remains in the nest for almost all of the incubation period and is fed both by the male and during short breaks. Incubation varies from 17 to 35 days, with larger species having longer incubation periods. The newly born young are altricial, either lacking feathers or with sparse white down. The young spend anything from three weeks to four months in the nest, depending on species, and may receive parental care for several months thereafter.[43]

As typical of K-selected species, the macaws and other larger parrot species have low reproductive rates. They require several years to reach maturity, produce one or very few young per year, and do not necessarily breed every year.

File:Sunconurepuzzle.jpgStudies with captive birds have given insight into which birds are the most intelligent. While parrots are able to mimic human speech, studies with the African Grey Parrot have shown that some are able to associate words with their meanings and form simple sentences (see Alex and N'kisi). Along with crows, ravens, and jays (family Corvidae), parrots are considered the most intelligent of birds. The brain-to body size ratio of psittacines and corvines is actually comparable to that of higher primates.[44] One argument against the supposed intelligent capabilities of bird species is that birds have a relatively small cerebral cortex, which is the part of the brain considered to be the main area of intelligence in other animals. However, birds use a different part of the brain, the medio-rostral neostriatum / hyperstriatum ventrale, as the seat of their intelligence. Not surprisingly, research has shown that these species tend to have the largest hyperstriata, and Dr Harvey J. Karten, a neuroscientist at the University of California, San Diego, who studied bird physiology, has discovered that the lower part of the avian brain is functionally similar to that in humans. Not only have parrots demonstrated intelligence through scientific testing of their language-using ability, but some species of parrot such as the Kea are also highly skilled at using tools and solving puzzles.[45]

Learning in early life is apparently important to all parrots, and much of that learning is social learning. Social interactions are often practised with siblings, and in several species creches are formed with several broods, and these as well are important for learning social skills. Foraging behaviour is generally learnt from parents, and can be a very protracted affair. Supra-generalists and specialists are generally independent of their parents much quicker than partly specialised species which may have to learn skills over a long period of time as various resources become seasonally available. Play forms a large part of learning in parrots; it can be solitary, and related to motor skills, or social. Species may engage in play fights or wild flights to practice predator evasion. An absence of stimuli can retard the development of young birds, as demonstrated by a group of Vasa Parrots kept in tiny cages with domesticated chickens from the age of 3 months; at 9 months these birds still behaved in the same way as 3 month olds, but had adopted some chicken behaviour.[29] In a similar fashion captive birds in zoo collections or pets can, if deprived of stimuli, develop stereotyped behaviours and harmful behaviours like self plucking. Aviculturists working with parrots have identified the need for environmental enrichment to keep parrots stimulated.

Many parrots can imitate human speech or other sounds. A study by Irene Pepperberg suggested a high learning ability in an African Grey Parrot named Alex. Alex was trained to use words to identify objects, describe them, count them, and even answer complex questions such as "How many red squares?" with over 80% accuracy. N'kisi, another African grey, has been shown to have a vocabulary of approximately a thousand words, and has displayed an ability to invent as well as use words in context and in the correct tense.

Parrots do not have vocal cords, so sound is accomplished by expelling air across the mouth of the bifurcated trachea. Different sounds are produced by changing the depth and shape of trachea. African Grey Parrots of all subspecies are known for their superior ability to imitate sounds and human speech. This ability has made them prized as pets from ancient time to the present. In the Masnavi, a writing by Rumi of Persia, AD 1250, the author talks about an ancient method for training parrots to speak.

Although most parrot species are able to imitate, some of the Amazon parrots are generally regarded as the next-best imitators and speakers of the parrot world. The question of why birds imitate remains open, but those that do often score very high on tests designed to measure problem solving ability. Wild African Grey Parrots have been observed imitating other birds.[46] Most other wild parrots have not been observed imitating other species.

The journal Animal Cognition stated that some birds preferred to work alone, while others like to work together as with African Grey Parrots. With two parrots, they know the order of tasks or when they should do something together at once, but they have trouble to exchanging roles. With three parrots, one parrot usually prefers to cooperate with one of the other two, but all of them are cooperating to solve the task.[47]

Humans and parrots have a complicated relationship. Economically they can be beneficial to communities as sources of income from the pet trade and are highly marketable tourism draws and symbols. But some species are also economically important pests, particularly some cockatoo species in Australia. Some parrots have also benefited from human changes to the environment in some instances, and have expanded their ranges alongside agricultural activity, but many species have declined as well.

There exist a number of careers and professions devoted to parrots. Zoos and aquariums employ keepers to care for and shape the behaviour of parrots. Some veterinarians who specialise in avian medicine will treat parrots exclusively. Biologists study parrot populations in the wild and help to conserve wild populations. Aviculturalists breed and sell parrots for the pet trade.

Tens of millions of parrots have been removed from the wild, and parrots have been traded in greater numbers and for far longer than any other group of wild animals.[48] Many parrot species are still threatened by this trade as well as habitat loss, predation by introduced species, and hunting for food or feathers. Some parrot species are agricultural pests,[49] eating fruits, grains, and other crops, but parrots can also benefit economies through birdwatching based ecotourism.[50]

Parrots are popular as pets due to their sociable and affectionate nature, intelligence, bright colours, and ability to imitate human voices. The domesticated Budgerigar, a small parrot, is the most popular of all pet bird species. In 1992 the newspaper USA Today published that there were 11 million pet birds in the United States alone,[51] many of them parrots. Europeans kept birds matching the description of the Rose-ringed Parakeet (or called the ring-necked parrot), documented particularly in a first century account by Pliny the Elder.[52] As they have been prized for thousands of years for their beauty and ability to talk, they have also often been misunderstood. For example, author Wolfgang de Grahl discusses in his 1987 book The Grey Parrot that some importers allowed parrots to drink only coffee while they were being shipped by boat considering pure water to be detrimental and believing that their actions would increase survival rates during shipping. (Nowadays it is commonly accepted that the caffeine in coffee is toxic to birds.)

Pet parrots may be kept in a cage or aviary; though generally, tame parrots should be allowed out regularly on a stand or gym. Depending on locality, parrots may be either wild caught or be captive bred, though in most areas without native parrots, pet parrots are captive bred. Parrot species that are commonly kept as pets include conures, macaws, Amazons, cockatoos, African Greys, lovebirds, cockatiels, Budgerigars, Eclectus, Caiques, parakeets, Pionus and Poicephalus. Species vary in their temperament, noise level, talking ability, cuddliness with people, and care needs, although how a parrot has been raised usually greatly affects its personality.

Parrots can make excellent companion animals, and can form close, affectionate bonds with their owners. However they invariably require an enormous amount of attention, care and intellectual stimulation to thrive, akin to that required by a three-year-old child, which many people find themselves unable to provide in the long term.[53] Parrots that are bred for pets may be hand fed or otherwise accustomed to interacting with people from a young age to help ensure they will be tame and trusting. However, parrots are not low maintenance pets; they require feeding, grooming, veterinary care, training, environmental enrichment through the provision of toys, exercise, and social interaction (with other parrots or humans) for good health.

Some large parrot species, including large cockatoos, amazons, and macaws, have very long lifespans, with 80 years being reported and record ages of over one hundred.[citation needed] Small parrots, such as lovebirds, hanging parrots, and budgies have shorter life spans of up to 15–20 years. Some parrot species can be quite loud, and many of the larger parrots can be destructive and require a very large cage, and a regular supply of new toys, branches, or other items to chew up. The intelligence of parrots means they are quick to learn tricks and other behaviours—both good and bad—that will get them what they want, such as attention or treats.

The popularity, longevity, and intelligence of many of the larger kinds of pet parrot has led to many birds needing to be re-homed during the course of their long lifespans. A common problem is that large parrots which are cuddly and gentle as juveniles will mature into intelligent, complex, often demanding adults that can outlive their owners. Due to these problems, and the fact that homeless parrots are not euthanised like dogs and cats, parrot adoption centres and sanctuaries are becoming more common.

Parrots have featured in human writings, story, art, humor, religion and music for thousands of years. From the Roman poet Ovid's "The Dead Parrot"(Latin),(English) to Monty Python's Dead Parrot Sketch millennia later, parrots have existed in the consciousness of many cultures. Recent books about parrots in human culture include Parrot Culture.[54]

In ancient times and current, parrot feathers have been used in ceremonies, and for decoration. The "idea" of the parrot has been used to represent the human condition in medieval literature such as the bestiary. They also have a long history as pets.

In Polynesian legend as current in the Marquesas Islands, the hero Laka/Aka is mentioned as having undertaken a long and dangerous voyage to Aotona in what are now the Cook Islands, to obtain the highly prized feathers of a red parrot as gifts for his son and daughter. On the voyage a hundred out of his 140 rowers died of hunger on their way, but the survivors reached Aotona and captured enough parrots to fill 140 bags with their feathers.[55] By at least some versions, the feathers were plucked off living parrots without killing them.[56]

Parrots are popular in Buddhist scripture and there are many writings about them. For example, Amitābha once changed itself into a parrot to aid in converting people. Another old story tells how after a forest caught fire, the parrot was so concerned it carried water to try and put out the flames. The ruler of heaven was so moved upon seeing the parrot's act, that he sent rain to put out the fire. In Chinese Buddhist iconography, a parrot is sometimes depicted hovering on the upper right side Guan Yin clasping a pearl or prayer beads in its beak.

Sayings about parrots colour the modern English language. The verb "parroting" can be found in the dictionary, and means "to repeat by rote." There are also clichés such as the British expression "sick as a parrot"; although this refers to extreme disappointment rather than illness, it may originate from the disease of psittacosis which can be passed to humans.[59][60] The first occurrence of a related expression is in Aphra Behn's 1681 play The False Count.[61]

Escaped parrots of several species have become established in the wild outside their natural ranges and in some cases outside the natural range of parrots. Among the earliest instances were pet Red Shining-parrots from Fiji which established a population on the islands of southern Tonga. These introductions were prehistoric and Red-shining Parrots were recorded in Tonga by Captain Cook in the 1770s.[23] Escapees first began breeding in cities in California, Texas and Florida in the 1950s (with unproven earlier claims dating back to the 1920s in Texas and Florida).[27] They have proved surprisingly hardy in adapting to conditions in Europe and North America. They sometimes even multiply to the point of becoming a nuisance or pest, and a threat to local ecosystems, and control measures have been used on some feral populations.[62]

Many parrot species are in decline and several are extinct. Of the 350 or so living species, 130 are listed as near threatened or worse by the IUCN of which 16 are currently considered Critically Endangered.[63] There are several reasons for the decline of so many species, the principal threats being habitat loss and degradation, hunting and, for certain species, the wild-bird trade. Parrots are persecuted because, in some areas, they are (or have been) hunted for food and feathers, and as agricultural pests. For a time, Argentina offered a bounty on Monk Parakeets (an agricultural pest), resulting in hundreds of thousands of birds being killed, though apparently this did not greatly affect the overall population.[64]

Capture for the pet trade is a threat to many of the rarer or slower to breed parrots. Habitat loss or degradation, most often for agriculture, is a threat to many species. Parrots, being cavity nesters, are vulnerable to the loss of nesting sites and to competition with introduced species for those sites. The loss of old trees is a particular problem in some areas, particularly in Australia where trees suitable for nesting need to be centuries old. Many parrots occur only on islands and are vulnerable to introduced species such as rats and cats, as they lack the appropriate anti-predator behaviours needed to deal with mammalian predators. Controlling such predators can help in maintaining or increasing the numbers of endangered species.[65] Insular species, which have small populations in restricted habitat, are also vulnerable to unpredictable events such as hurricanes and volcanic eruptions.

There are many active conservation groups whose goal is the conservation of wild parrot populations. One of the largest is the World Parrot Trust,[66] an international organisation. The group gives assistance to worthwhile projects as well as producing a magazine[67] and raising funds through donations and memberships, often from pet parrot owners. They state they have helped conservation work in 22 countries. On a smaller scale local parrot clubs will raise money to donate to a conservation cause. Zoo and wildlife centres usually provide public education, to change habits that cause damage to wild populations. Recent conservation measures to conserve the habitats of some of the high-profile charismatic parrot species has also protected many of the less charismatic species living in the ecosystem.[7] A popular attraction that many zoos employ is a feeding station for lories and lorikeets, where visitors feed small parrots with cups of liquid food. This is usually done in association with educational signs and lectures.

Several projects aimed specifically at parrot conservation have met with success. Translocation of vulnerable Kakapo, followed by intensive management and supplementary feeding, has increased the population from 50 individuals to 123.[68] In New Caledonia the Ouvea Parakeet was threatened by trapping for the pet trade and loss of habitat. Community based conservation, which eliminated the threat of poaching, has allowed the population to increase from around 600 birds in 1993 to over 2000 birds in 2009.[69]

At present the IUCN recognises 19 species of parrot as extinct since 1600 (the date used to denote modern extinctions).[70] This does not include species like the New Caledonian Lorikeet which has not been officially seen for 100 years yet is still listed as critically endangered.

Trade, export and import of all wild-caught parrots is regulated and only permitted under special licensed circumstances in countries party to CITES, the Convention on the International Trade in Endangered Species, that came into force in 1975 to regulate the international trade of all endangered wild caught animal and plant species. In 1975, 24 parrot species were included on Appendix I of CITES, thus prohibiting commercial international trade in these birds. Since that initial listing, continuing threats from international trade led CITES to add an additional 32 parrot varieties to Appendix I.[71] All the other parrot species are protected on Appendix II of CITES. In addition, individual countries may have laws to regulate trade in certain species.

↑ 13.013.113.2de Kloet, RS, de Kloet SR (2005). The evolution of the spindlin gene in birds: Sequence analysis of an intron of the spindlin W and Z gene reveals four major divisions of the Psittaciformes. Molecular Phylogenetics and Evolution36 (3): 706–721.

↑ (2006). Population size, provisioning frequency, flock size and foraging range at the largest known colony of Psittaciformes: the Burrowing Parrots of the north-eastern Patagonian coastal cliffs. Emu106 (1): 69–79.